Recovery of petroleum oil from partially depleted subterranean reservoirs



United States Patent RECOVERY OF PETROLEUM OIL FROM PAR- TIALLY DEPLETED SUBTERRANEAN RESER- VOIRS Paul B. Crawford, Bryan, Tex.

No Drawing. Application April 20, 1955, Serial No. 502,743

44 Claims. (Cl. 16611) This invention relates to secondary recovery of petroleum oil from subterranean reservoirs and relates more particularly to the method involving combustion of petroleum oil remaining in partially depleted subterranean reservoirs to assist in recovery of a portion of such remaining oil.

Petroleum oil is usually recovered from subterranean reservoirs initially as a result of gas pressure, rock pressure, or natural water drive which forces the oil from the oil-bearing formation or reservoir through the producing well to the surface. As recovery of oil from the reservoir continues, the reservoir energy gradually decreases an finally becomes insufiicient to force the oil to the surface, although a major portion of the original quantity of the oil remains in the reservoir. To increase the ultimate recovery of the oil, pumping is then employed, but when the rate of recovery by pumping falls to an uneconomically low level, a further increase in the ultimate recovery of the oil may still be economically effected by the employment of secondary recovery methods such as gas drive or water drive. It has recently been proposed to increase the ultimate recovery of the oil by combustion or burning of a part of the oil in place in the reservoir, the combustion being supported by injection of air or other oxidizing gas through an input well or wells, whereby, as a result of decreased viscosity, distillation, and viscosity breaking, the unburned oil, along with distillation and viscosity breaking products, is carried to and recovered from an output well or group of output Wells.

In the subterranean combustion process, the oxidizing gas, which may be air, oxygen, oxygen-enriched air, air admixed with inert gas to reduce the proportion of oxygen, oxygen admixed with inert gas, or any other suitable oxidizing gas or mixture which will support combustion within the subterranean reservoir, is passed, as by pumping, through an input well to the reservoir in which the combustion process is to be effected and combustion within the reservoir is initiated by suitable means. The flow of oxidizing gas to the reservoir is continued and the combustion gases, oil, and the distillation and viscosity breaking products migrate in front of the combustion zone to an output well or wells leading from the reservoir, from which output well or wells these fluids are removed and thereafter treated for recovery of the desired valuable constituents. The heated fluids migrating in front of the combustion zone strip the oilbearing sand of the greater portion of the oil leaving behind within the sand a carbonaceous hydrocarbon deposit. The carbonaceous deposit essentially is the fuel consumed in the process and combustion of the carbonaceous deposit continues until the deposit has been substantially entirely consumed. The carbonaceous deposit preferentially burns to form carbon dioxide irrespective of restriction in the supply of oxidizing gas and thereby provides a maximum amount of energy per unit amount of carbonaceous deposit consumed. However, where the 2,804,146 Patented Aug. 27, 1957 ice amount of carbonaceous deposit is in excess of about 2 percent by weight of the sand, combustion of the carbonaceous deposit provides more than suilicient thermal energy for achieving efficient recovery of petroleum oil by the combustion process, and the additional amount of oxidizing gas consumed by the carbonaceous deposit constitutes an economic waste not only with respect to the excessive amounts of oxidizing gas which must be pumped to the reservoir but also with respect to the excess pump capacity required.

It is an object of this invention to reduce the quantity of oxidizing gas required for carrying out recovery of petroleum oil from a partially depleted subterranean reservoir by the combustion process. It is another object of this invention to reduce the cost of recovering petroleum oil by the combustion process. It is another object of this invention to reduce the pumping capacity required for recovery of petroleum oil by the combustion process. It is another object of this invention to increase the yield of valuable products obtained by the combustion process. Other objects of the invention will become apparent from the following description thereof.

In accordance with the invention, to the oxidizing medium passed to a partially depleted subterranean oil reservoir undergoing combustion for the purpose of increasing the ultimate recovcry of oil therefrom is added a catalyst to increase the ratio of carbon monoxide to carbon dioxide in the gas produced by combustion. The catalyst is a fluid phase, chlorine-containing material. Preferred catalysts are phosphorous trichloride, phosphorous oxychloride, chlorine, hydrogen chloride, and the chlorine derivatives of methane. By the chlorine derivatives of methane, I mean monochloromethane, dichloromethane, trichloromethane, and tetrachloromethane.

By the addition of the chlorine-containing catalyst to the air or other oxidizing gas passed to a subterranean reservoir wherein combustion has been effected to increase the ultimate yield of petroleum oil, burning of the carbonaceous deposit with preferential formation of carbon monoxide and hydrogen results. Since combustion with formation of carbon monoxide and hydrogen requires less oxygen than combustion with formation of carbon dioxide and water, as indicated in the following equations:

a lesser amount of oxidizing gas is required as the proportion of carbon monoxide and hydrogen in the combustion products increases. As a result, pumping costs, as well as the required pumping capacity, are decreased. Further, the fluid products recovered from the output well or wells will contain carbon monoxide and hydrogen which may be utilized to manufacture chemicals or synthetic fuels or utilized as a fuel gas of low alorific value.

The fluid phase, chlorineccntaining materials are gaseous or liquid at atmospheric conditions of tempera ture and pressure. Accordingly, the catalyst may be added in the liquid phase or the gaseous phase to the oxidizing gas pumped to the reservoir undergoing combustion. Preferably, however, the catalyst is admixed with the oxidizing gas in the vapor phase. Where the catalyst is in the liquid phase at atmospheric conditions of temperature and pressure, a convenient method for effecting mixture is to pass the oxidizing gas or, preferably, a portion of the oxidizing gas, through a bath of the liquid catalyst prior to passage to the input well whereby the oxidizing gas will vaporize a portion of the liquid catalyst carrying the vaporized portion along with it to the input well. Proportiouing of the oxidizing gas and liquid phase may be effected by any desired means. A simple means of proportioning involves passing a known portion of the oxidizing gas through a bath of the liquid phase catalyst at a known temperature whereby the proportion of catalyst vaporizing in the oxidizing gas will be equal to the ratio of the vapor pressure of the catalyst at the known temperature to the total pressure of the oxidizing gas after admixture with the catalyst. Where the catalyst is in the gaseous phase, the gaseous catalyst may simply be admixed in the proper proportion with the oxidizing gas and, for this purpose, any suitable conventional means of gas proportioning may be employed.

The proportion of carbon monoxide to carbon dioxide, in the gases produced by combustion of the carbonaceous deposits, depends upon the concentration of catalyst employed. The proportion of hydrogen to water produced by combustion of the carbonaceous deposits also depends upon the concentration of catalyst employed, although to a lesser extent. Concentrations of at least 0.2 percent by volume in the gaseous phase may be employed although it is preferred to employ concentrations of at least 0.3 percent by volume in the gaseous phase. Higher concentrations may be employed to obtain higher ratios of carbon monoxide to carbon dioxide. However, it is not possible to suppress completely the formation of carbon dioxide and, accordingly, it is preferred not to employ concentrations greater than 1.6 percent by volume in the gaseous phase since above this concentration the increase in the proportion of carbon monoxide to carbon dioxide with increasing concentration of catalyst is negligible. Generally, concentrations of catalyst between 0.3 and 1.5 percent by volume in the gaseous phase give satisfactory results.

Where the fluid phase, chlorine-containing catalyst is added to the oxidizing gas passed to the reservoir undergoing combustion, the fluids recovered from an output well will retain to an appreciable extent the activity of the catalyst to etfect preferential formation of carbon monoxide and hydrogen. In accordance with a particular embodiment of the invention, fluids, either liquids or gases, recovered from a subterranean reservoir in which combustion, with the addition of the catalyst to the oxidizing gas, has been effected to increase the ultimate recovery of petroleum oil therefrom, are admixed with the oxidizing gas passed to the input well or another well leading to the same or another subterranean reservoir being treated by the combustion process. In carrying out this procedure, a portion of the fluids from the output well, without any treatment for recovery and removal of any of the constituents thereof, may be admixed with the oxidizing gas, or the fluids or a portion thereof from the output well after treatment for removal and recovery of petroleum hydrocarbons, and removal and recovery of carbon monoxide and hydrogen where it is desired to recover the carbon monoxide and hydrogen, may be admixed with the oxidizing gas. By recycle of fluid from an output well to an input well leading to the same reservoir or to another reservoir, a saving in the amount of catalyst employed is effected since the amount of catalyst added to the oxidizing gas is reduced in proportion to the amount and the activity of the catalytically acting constituent in the fluid from the output well that is added to the oxidizing gas.

This application constitutes a consolidation of my prior co-pending applications Serial Nos. 138,511 and 138,512, both filed January 13, 1950, and both now abandoned, and therefore bears the relationship of continuation-in-part application with respect to each of those prior applications.

Having thus described my invention, it will be understood that such description has been given by way of illustration and example, and not by way of limitation, reference for the latter purpose being had to the appended claims.

I claim:

1. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir a chlorine-containing catalyst to increase the ratio of carbon monoxide to carbon dioxide in the gas produced by combustion.

2. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizng gas is passed to said reservoir through an input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir a fluid phase, chlorinecontaining material.

3. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir a material selected from the groups consisting of phosphorous trichloride and phosphorous oxychloride, and chlorine, hydrogen chloride, and the chlorine derivatives of methane.

4. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well, combustion of a portion of the petroleum oil is maintained within said reservoir, and petroleum products and combustion products are withdrawn from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir a fluid phase, chlorine-containing material, and admixing at least a portion of the fluid products withdrawn through said output well from said reservoir with oxidizing gas passed to a subterranean petroleum oil reservoir undergoing combustion for recovery of petroleum oil therefrom.

5. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well, combustion of a portion of the petroleum oil is maintained within said reservoir, and petroleum products and combustion products are withdrawn from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir a material selected from the groups consisting of phosphorous trichloride and phosphorous oxychloride and chlorine, hydrogen chloride, and the chlorine derivatives of methane, and admixing at least a portion of the fluid products withdrawn through said output well from said reservoir with oxidizing gas passed to a subterranean petroleum oil reservoir undergoing combustion for recovery of petroleum oil therefrom.

6. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir a compound selected from the group consisting of phosphorous trichloride and phosphorous oxychloride.

7. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir in a concentration of at least 0.2 percent by volume in the gaseous phase a compound selected from the group consisting of phosphorous trichloride and phosphorous oxychloride.

8. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir in a concentration between about 0.2 and 1.6 percent by volume in the gaseous phase a compound selected from the group consisting of phosphorous trichloride and phosphorous oxychloride.

9. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir in a concentration between about 0.3 to 1.5 percent by volume in the gaseous phase a compound selected from the group consisting of phosphorous trichloride and phosphorous oxychloride.

10. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir phosphorous trichloride.

11. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir in a concentration of at least 0.2 percent by volume in the gaseous phase phosphorous trichloride.

12. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through on input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the impovement comprising adding to said oxidizing gas passed to said reservoir in a concentration between about 01 and 1.6 percent by volume in the gaseous phase phosphorous trichloride.

13. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input weil and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir in a concentration between about 0.3 and 1.5 percent by volume in the gaseous phase phosphorous trichloride.

14. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir phosphorous oxychloride.

15. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir in a concentration of at least 0.2 percent by volume in the gaseous phase phosphorous oxychloride.

16. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir in a concentration between about 0.2 and 1.6 percent by volume in the gaseous phase phosphorous oxychloride.

17. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir in a concentration between about 0.3 and 1.5 percent by volume in the gaseous phase phosphorous oxychloride.

18. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well, combustion of a portion of the petroleum oil is maintained within said reservoir, and petroleum products and combustion products are withdrawn from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir a chlorine-containing catalyst to increase the ratio of carbon monoxide to carbon dioxide in the gas produced by combustion of the petroleum oil, and admixing at least a portion of the fluid products withdrawn through said outlet well from said reservoir with oxidizing gas passed to a subterranean petroleum oil reservoir undergoing combustion for recovery of petroleum oil therefrom.

19. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well, combustion of a portion of the petroleum oil is maintained within said reservoir, and petroleum products and combustion products are withdrawn from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir a chlorine containing catalyst to increase the ratio of carbon monoxide to carbon dioxide 7 in the gas produced by combustion of the petroleum oil, and recycling at least a portion of the fiuid products withdrawn through said outlet well from said reservoir to said inlet well for admixture with oxidizing gas passed therein.

20. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well, combustion of a portion of the petroleum oil is maintained within said reservoir, and petroleum products and combustion products are withdrawn from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir a compound selected from the group consisting of phosphorous trichloride and phosphorous oxychloride, and admixing at least a portion of the fluid products withdrawn through said outlet well from said reservoir with oxidizing gas passed to a petroleum oil reservoir undergoing combustion for recovery of petroleum oil therefrom.

21. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well, combustion of a portion of the petroleum oil is maintained within said reservoir, and petroleum products and combustion products are withdrawn from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir a compound selected from the group consisting of phosphorous trichloride and phosphorous oxychloride, and recycling at least a portion of the fluid products withdrawn through said outlet well from said reservoir to said inlet well for admixture with oxidizing gas passed therein.

22. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir a material selected from the group consisting of chlorine, hydrogen chloride, and the chlorine derivatives of methane.

23. The process of claim 22 wherein said material added to said oxidizing gas passed to said reservoir is a chlorine derivative of methane.

24. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir in a concentration of at least 0.2 percent by volume in the gaseous phase a material selected from the group consisting of chlorine, hydrogen chloride, and the chlorine derivatives of methane.

25. The process of claim 26 wherein said material added to said oxidizing gas passed to said reservoir is a chlorine derivative of methane.

26. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir in a concentration between about 0.2 to 1.6 percent by volume in the gaseous phase a material selected from the group consisting of chlorine, hydrogen chloride, and the chlorine derivatives of methane.

27. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well and combustion of a portion of the petroleum oil is maintained within said reservoir for the purpose of withdrawing petroleum products and combustion products from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir in a concentration between about 0.3 and 1.5 per cent by volume in the gaseous phase a material selected from the group consisting of chlorine, hydrogen chloride, and the chlorine derivatives of methane.

28. The process of claim 22 wherein said material added to said oxidizing gas passed to said reservoir is chlorine.

29. The process of claim 22 wherein said material added to said oxidizing gas passed to said reservoir is tetrachloromethane.

30. The process of claim 22 wherein said material added to said oxidizing gas passed to said reservoir is trichloromethane.

31. The process of claim 22 wherein said material added to said oxidizing gas passed to said reservoir is dichloromethane.

32. The process of claim 22 wherein said material added to said oxidizing gas passed to said reservoir is hydrogen chloride.

33. The process of claim 26 wherein said material added to said oxidizing gas passed to said reservoir is chlorine.

34. The process of claim 26 wherein said material added to said oxidizing gas passed to said reservoir is tetrachloromethane.

35. The process of claim 26 wherein said material added to said oxidizing gas passed to said reservoir is trichloromethane.

36. The process of claim 26 wherein said material added to said oxidizing gas passed to said reservoir is dichloromethane.

37. The process of claim 26 wherein said material added to said oxidizing gas passed to said reservoir is hydrogen chloride.

38. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input well, combustion of a portion of the petroleum oil is maintained within said reservoir, and petroleum products and combustion products are withdrawn from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir a material selected from the group consisting of chlorine, hydrogen chloride, and the chlorine derivatives of methane, and admixing at least a portion of the fluid products withdrawn through said outlet well from said reservoir with oxidizing gas passed to a subterranean petroleum oil reservoir undergoing combustion for recovery of petroleum oil therefrom.

39. The process of claim 38 wherein said material added to said oxidizing gas passed to said reservoir is chlorine.

40. The process of claim 38 wherein said material added to said oxidizing gas passed to said reservoir is tetrachloromethane.

41. The process of claim 38 wherein said material added to said oxidizing gas passed to said reservoir is trichloromethane.

42. The process of claim 38 wherein said material added to said oxidizing gas passed to said reservoir is dichloromethane.

43. The process of claim 38 wherein said material added to said oxidizing gas passed to said reservoir is hydrogen chloride.

44. In a process for the recovery of petroleum oil from a partially depleted subterranean petroleum oil reservoir wherein an oxidizing gas is passed to said reservoir through an input Well, combustion of a portion of the petroleum oil is maintained within said reservoir, and petroleum products and combustion products are withdrawn from said reservoir through an output well, the improvement comprising adding to said oxidizing gas passed to said reservoir a material selected from the group consisting of chlorine, hydrogen chloride, and the chlorine derivatives of methane, and recycling at least a portion of the fluid products withdrawn through said 10 outlet well from said reservoir to said inlet well for admixture with oxidizing gas passed therein.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A PROCESS FOR THE RECOVERY OF PETROLEUM OIL FROM A PARTIALLY DEPLETED SUBTERRANEAN PETROLEUM OIL RESERVOIR WHEREIN AN OXIDATION GAS IS PASSED TO SAID RESERVOIR THROUGH AN INPUT WELL AND COMBUSTION OF A PORTION OF THE PETROLEUM OIL IS MAINTAINED WITHIN SAID RESERVOIR FOR THE PURPOSE OF WITHDRAWING PETROLEUM PRODUCTS AND COMBUSTION PRODUCTS FROM SAID RESERVOIR THROUGH AN OUTPUT WELL, THE IMPROVEMENT COMPRISING ADDING TO SAID OXIDIZING GAS PASSED TO SAID RESERVOIR A CHLORINE-CONTAINING CATALYST TO INCREASE THE RATIO OF CARBON MONOXIDE TO CARBON DIOXIDE IN THE GAS PRODUCED BY COMBUSTION. 